The invention relates to a control system for controlling the driven wheel speeds of a vehicle with steerable wheels and independently driven wheels.
Zero turn radius vehicles, such as lawn mowers and windrowers, have relied on caster wheels and some form of independent control of the drive wheels for steering. Such designs can result in poor directional control when traversing side slopes and can limit the usability of the vehicle. Certain known Ackerman-type steering linkages with 180 degrees of wheel turning capability have been unduly complicated and have included exposed gears. A steering mechanism for a front wheel drive vehicle is shown in the article xe2x80x9cA 180xc2x0 steering interval mechanismxe2x80x9d by E. Chicurel in xe2x80x9cMechanism and Machine Theoryxe2x80x9d Vol. 34, No. 3, April 1999. However, this article does not disclose how driven wheel speed could be controlled to achieve a zero turn radius.
Accordingly, an object of this invention is to provide a driven wheel drive speed control system for a vehicle with steerable wheels and independently driven wheels.
A further object of the invention is to provide such a system which results in a constant travel speed of a center of the steerable wheel axle.
Another object of the invention is to provide such a system which reduces the chances of vehicle tipping during a turn.
Another object of the invention is to provide such a system for use with a vehicle with zero turn radius capability.
These and other objects are achieved by the present invention, wherein a control system controls the speed of the driven wheels of a vehicle having an operator controlled steering wheel, an operator controlled speed command device, steerable wheels and driven wheels. The control system includes a steering angle sensor coupled to the steering input member and generating a steering angle signal, a speed command sensor coupled to the speed command device and generating a speed command signal, and a control unit. The control unit generates driven wheel speed command signals as a function of the steering angle signal, a wheelbase of the vehicle, a distance between the driven wheels, and the speed command signal. The magnitude of the speed command signal is limited to a calculated limit value which is a function of the wheelbase of the vehicle, a distance from a driven wheel axle of the vehicle forward to a center of gravity of the vehicle, a value representing a maximum allowable centripetal acceleration, and the steering angle signal. The control system automatically reduces speed when the vehicle enters a sharp turn, thus reducing the chances of lateral tipping without compromising either travel speed or turning radius. This control system can be used with vehicles with zero turn radius capability, since the driven wheel speed command signals are determined by calculations which do not require dividing by a turn radius value.